1. Technical Field
The present invention relates to a piezoelectric device, a liquid ejection head, and a method of manufacturing the piezoelectric device, the piezoelectric device including a first substrate having an empty chamber and a piezoelectric element formed on a diaphragm that defines the empty chamber.
2. Related Art
Piezoelectric devices including piezoelectric elements have various applications, for example, liquid ejecting apparatuses and vibration sensors. For example, a liquid ejecting apparatus ejects (discharges) various kinds of liquids from a liquid ejection head by using the piezoelectric device. Examples of liquid ejecting apparatuses include image recording apparatuses such as ink jet printers and ink jet plotters. In recent years, liquid ejecting apparatuses that have the capability of accurately discharging a very small amount of liquid at predetermined positions have been provided in various manufacturing apparatuses. These applications include, for example, display manufacturing apparatuses for manufacturing color filters for liquid crystal displays, electrode forming apparatuses for forming electrodes for organic electroluminescence (EL) displays and field emission displays (FEDs), and chip manufacturing apparatuses for manufacturing biochips (biochemical chips). A recording head for image recording apparatuses ejects liquid ink, and a color material ejection head for display manufacturing apparatuses ejects solutions of individual coloring materials of red (R), green (G), and blue (B). An electrode material ejection head for the electrode forming apparatus ejects a liquid electrode material, and a bio-organic compound ejection head for chip manufacturing apparatuses ejects a solution of bio-organic compounds.
The liquid ejection head having the piezoelectric device includes a plurality of nozzles, and pressure chambers and piezoelectric elements corresponding to each individual nozzle. The pressure chamber is formed by etching a substrate (actuator substrate), and a part of the pressure chamber is defined by a flexible diaphragm. On the diaphragm, a piezoelectric element that includes a lower electrode layer, a piezoelectric layer of a piezoelectric material such as titanate zirconate (PZT), and an upper electrode layer is formed. A communication substrate is bonded to the opposite side of the pressure chamber-formed substrate, and the pressure chamber communicates with the nozzle via a nozzle communication path formed in the communication substrate. The liquid ejection head of the structure applies a voltage to deform the pressure chambers corresponding to the respective nozzles to cause a pressure variation to be generated in the liquid in the corresponding pressure chambers so as to eject the liquid from the nozzles (see, for example, JP-A-2015-89614).
The tendency to downsize the liquid ejection heads has led to the thickness of pressure chamber-formed substrates being decreased. These thinner substrates decrease the stiffness of the pressure chamber-formed substrate, and the substrates can be readily deformed. In particular, a partition wall that defines adjacent pressure chambers in the pressure chamber-formed substrate has been downsized in the pressure chamber array direction due to the recent increased packaging density that has led to the narrowed pitch of the pressure chambers. Consequently, the stiffness of the partition wall defining the pressure chambers has been decreasing. This decreased stiffness enables the pressure chamber-formed substrate to be readily deformed and may cause separation of the pressure chamber-formed substrate and the communication substrate that is bonded to the substrate. For example, as shown in a recording head 100 illustrated in FIG. 12, a multilayered piezoelectric element 90 may be deformed in a direction opposite to a pressure chamber 91 in an initial state (in a state in which no voltage is being applied), for example, due to a tensile force caused by the layers (films) constituting the piezoelectric element 90. If the deformation is transmitted to a part of a pressure chamber-formed substrate 93 that defines the periphery of the pressure chamber 91 via a diaphragm 92, especially, the pressure chamber-formed substrate 93 (that is, the partition wall portion that defines the pressure chamber 91) on the periphery of the pressure chamber 91 deforms to curve toward the piezoelectric element 90. Due to this deformation, for example, the adhesive that bonds the pressure chamber-formed substrate 93 and the communication substrate 94 comes off, and a part of the pressure chamber-formed substrate 93 may be separated from the communication substrate 94. Such a problem may similarly occur in other piezoelectric devices that include a first substrate formed by providing a piezoelectric element above an empty chamber and a second substrate that is bonded to the first substrate.